Musnad Abu Ya'la al-Mawsili 115:206

Zuhayr narrated to us, Wahb ibn Jarir narrated to us, my father narrated to us, he said: I heard Qatadah say: I asked Anas ibn Malik, "How was the recitation of the Messenger of Allah (may Allah bless him and grant him peace)?" He said: "He used to extend it with an extension."